Material retaining end plate for roller mills



Oct. 27, 1953 c. P. BRASINGTON 2,656,

MATERIAL RETAINING END PLATES FOR ROLLER MILLS File i June 13, 1952 2 Sheets-Sheet l IN V EN TOR.

ATTORNEYS.

Oct. 27, 1953 c. P. BRASINGTON 2,656,936

MATERIAL RETAINING END PLATES FOR ROLLER MILLS Filed June 15, 1952 2 Shets-Sheet 2 Eg/l IN V EN TOR.

A TTORNE Y5 MPW Patented Oct. 27, 1953 UNITED STATES PATENT OFFICE MATERIAL RETAINING END PLATE FOR ROLLER MILLS This invention relates to pigment grinding mills of the type used in ink and paint manufacturing, and more particularly is directed to end plates for controlling the distribution of thematerial being ground over the surface of the rollers.

A typical grinding mill of this type includes three parallel rollers with a substantial quantity of material generally consisting of a pigment and its vehicle being placed between the first and middle rollers. The middle roller is rotated at a higher speed than the first roller so that, as the material passes downwardly between the rollers, the greater portion of it adheres to the middle roller. The material picked up by the middle roller then passes upwardly between the middle and third rollers and adheres to the third roller which is rotated at a still higher rate of speed. A scraper blade engages the third or terminal roller, separating the pigment and directing it into a suitable container.

As previously pointed out in my earlier Patent No. 2,063,363 on a Grinding Mill, one of the principal problems inherent in the operation of a pigment grinding mill is the prevention of endwise leakage of the pigment past the edges of the rollers. The solution proposed in that patent involves the suspension of two end plates, or gates between the first and second rollers. These plates are mounted inwardly of the ends of the rollers and are configurated at their lower edges to form two curves of a radius only slightly larger than the radius of the rollers. The two curves meet in an apex and the relatively heavy plates are carefully balanced so that this apex is dis posed directly over the line of contact with the rollers, leaving a small clearance of the order of fifteen or twenty thousandths of an inch be tween the rollers and end plates.

The end plates function to constrain the greater portion of the material between them while allowing a predetermined amount to leak through the small clearance spaces and escape toward the end of the rollers. The amount of material allowed to escape and the displacement of the end plates inwardly from the ends of the rollers are correlated so that all of the material passing laterally beyond the plates is picked up by the second roller and transferred to the succeeding rollers and none of it flows out beyond the roller ends.

These plates have generally proven very effective in operation. However, recently with the advent of grinding mills having a higher speed of roller rotation, certain new difficulties have manifested themselves. These diificulties include accelerated abrasion of the end plates and adjacent areas of the rollers and excessive leakage of material toward the end of the rollers. No apparent explanation for these difficulties could be found; but after considerable investigation, I have discovered that these difiiculties result from the fact that the increased speed of rotation of the mill rollers causes a pressure differential to be built up between the material in contact with one side of the end plates and the material in contact with the other side. That is, there is an unequal pressure condition established in the material. passing between the end plates and the first roller as compared with the material passing between the end plates and the second roller. The increased speed of rotation causes. a turbulent condition to be set up in the material flowing between the plates and rollers. This turbulence is greater near the faster moving, second roller and results in a decreased. pressure area, somewhat similar to that of the Bernoulli effect, between the plates and middle roller. This pressure condition is exactly the reverse of that which would be expected, since normally the more rapidly rotating roller would tend to force more material against the under surface of. the plates causing a higher pressure to be developed in the layer of material between the second roller and the plates.

The pressure on the side of the end plate facing the slower moving first roller exceeds that on theportion of the plate facing the middle roller by an amount sufiicient to cause the heavy end plate, which is normally balanced so that its apex resides directly over the line of contact of the rollers, to be drawn toward the faster moving middle roller. This results in a grinding action between the plates and adjacent roller area causing the accelerated abrasion of both the plate and roller. Furthermore, the carefully adjusted clearance space between the plates and the two rollers is not maintained; the rollers and end plates are properly spaced only when the plates hang vertically, and if they shift to some other position, an excess of material will flow along one roller.

The present invention is predicated upon the discovery of this hitherto unrecognized pressure and the provision of means for eliminating its deleterious effects. More specifically, it is the principal concept of this invention to bias the end plates so that they are urged in the direction of contact with the middle roller, and then to provide an adjustable stop'means for preventing the displacement of theplates beyond. a pre-- determined position in which their apexes are disposed over the line of contact. In this way the plates are always maintained in their position of optimum efiectiveness in which they are spaced a predetermined distance from each of the rollers. By providing a small biasing force in the direction in which the plates are urged during high speed operation and a stop for limiting the displacement of the plates in this direction, the plates will continue to be correctly disposed even if the roller speed should be decreased reducing the pressure diiferential existing in the pigment films between the plates and the first and middle rollers. That is, the small biasing force is sufficient to hold the plates against the stop even in the absence of the pressure diiferential built up during high speed operation, so that the plate position will be determined by the position of the stop irrespective of roller speed.

It is another object of this invention to provide an improved plate mounting structure which will not only facilitate the accurate alignment of the plates with the rolls but which will also minimize the possibility of the plates or rolls being inadvertently damaged during cleaning. Generally, the plate mounting structure is such that the plates may be pivoted upwardly into an upswung position, in which the roller surfaces beneath the plates are rendered accessible for wiping off and cleaning. One difficulty with mounting structures of the type shown in my previous patent is that, if a plate is jarred during the cleaning process, it tends to pivot about the connection provided for its vertical adjustment, and when the plate is swung downwardly, back into its vertical position, the apex is apt to strike one of the rollers nicking the roller or chipping the plate, or both. This problem is overcome in the present mounting structure by providing new and improved adjusting means which allow the height of the plate above the rollers to be varied but prevent the plate from pivoting in its upswung position, even if it should be accidentally jarred.

Other objects and advantages of the present invention will be more readily apparent from a further consideration of the following detailed description of the drawings showing a preferred embodiment of the invention.

In the drawings:

Figure 1 is a front elevational view of a grinding mill provided with end plates constructed in accordance with the present invention.

Figure 2 is an enlarged fragmentary sectional View through an end plate and its mounting structure.

Figure 3 is a perspective view of an end plate and its associated mounting structure.

Figure 4 is an end view with the drive mechanism and roller bearings being removed to show the relationship of the end plate, rolls and mounting structure.

Figure 5 is a cross sectional View taken on 55 of Figure 3.

As shown, the end plates of the present invention are employed in conjunction with a three roll pigment grinding mill. This particular type of mill is chosen merely for purposes of illustration, and the present invention is equally adaptable for use with a pigment grinding mill having 3, 5, or, in fact, any number of rollers.

In the embodiment shown, three grinding rollers H], H and I2 are rotatably mounted in bearings |3 supported by frame member M. A motor, not shown, drives the rollers through some suitable mechanism such as gear train l5. As indicated in Figure 4, the rollers are driven so that adjacent rollers always rotate in opposite directions.

The central roller I is mounted in fixed bearings and the position of the first roller l0 and the final roller |2 may be varied relative to the central roller H in order to alter the bearing pressure between the rollers. This adjustment may be effectuated through handles |6-|6 and screws H. No further details of the roll mounting and frame construction will be given since these elements constitute no part of the present invention.

The end plates, or gates, |B are suspended over the first and middle rollers from rod 20. Rod is journalled in frame members 2| and 22 and is preferably threaded as at 23 and 24. A bearing 25 is attached to cross piece 25 of the frame and supports the center portion of rod 20. In the preferred embodiment, rod 29 is disposed on a line displaced from the vertical plane extending through the line of contact of the first and middle rollers, in the direction of the center of the second or middle roller.

The mounting structure by means of which each of the end plates [8 is suspended from the rod 20 includes an arm 21 having a vertically extending straight portion 28, an arcuate portion 30 and an offset threaded boss 3| for engaging rod 20. Arm 2? is provided with an inwardly extending lug 32 to which mounting bracket 33 is pivotally connected by means of pin 34. Bracket 33 includes ears 35 embracing lug 32, extension 39 and a depending foot 35 which is joined to the end plate by means of bolt 31. The end plate [8 extends substantially from the center of the first roll I!) to the center of the second roll II, the lower edge of the plate being configurated to form two partial circles concentric with the rolls and of a slightly larger radius. These two curves meet at an apex 38 which is preferably disposed directly over the line of contact of the two rolls.

In order to maintain apex 38 in its correct position despite the pressure differential built up in the pigment material passing between the plate and the rollers, which pressure differential tends to force the plate toward the second roller (counterclockwise in Figure 4), stop means are provided for limiting the displacement of the plate in this direction. The stop means, in the preferred embodiment, include flange 40 of cross piece 26 and a set screw 4| which is carried by arm 21 and abuts the flange 40. Obviously, any straight abutment member can be used in cooperation with a set screw 4| and this member need not be constituted by a flange of cross piece 26. Additionally, to assure correct positioning of the plate even in the absence of any pressure in the pigment material, as would be the case when the mill rolls are operated at relatively low speeds, the plate is biased so that it inherently tends to rotate toward the middle roller, thereby causing set screws 4| to remain in engagement with flange 40. In the preferred embodiment, the plate is biased by offsetting boss 3| from mounting arm 21 so that when the plate is vertically disposed its center of gravity does not lie be! neath rod 20, and the plate thereby tends to rotate toward the first roller, Flange 40 extends across the top of the mill parallel to rod 20 and lies on the same side of the rod as the middle roller Set screw 4| is threaded in a suitable opening in arm 2'! and by varying the length of the screw protruding beyond the opening, the position of the plate H; can be accurately ad- Justed.

End plates I8 can be shifted inwardly or outwardly along the rollers by rotating rod 20 by means of handle 42; threaded portions 23 and 2d of rod 20 are preferably threaded in the reverse direction so that when rod 20 is turned both plates are simultaneously advanced toward or retracted from the ends of the rolls. In order to adjust the clearance space between plate l8 and the rolls, depending foot 36 of bracket 33 is provided with a vertical slot for receiving bolt 31 which threadably engages plate 18. Plate [8 can be raised or lowered by loosening bolt 31 and set screw 43 which is carried by extension 39 and abuts the upper rim of the end plate. After the plate is brought into the desired position, both bolt 31 and set screw 43 can be tightened down to hold it in place.

In order to prevent rotation of the end plate about bolt 37, the rear surface of the plate is provided with two flanges 44 and 45 which embrace foot 36 of bracket 33, constraining the plate to vertical movement. Hence even during the time that the plate is raised for cleaning (by pivoting it upwardly about pin 34), it will not be displaced by a sideward blow but will return to precisely the same position when again lowered. Consequently, even under rough handling, apex 38 will not nick either of the rollers or be chipped itself, thereby necessitating the refinishing of the damaged surface.

The plates can be secured in their upswung cleaning position by means of latch arm 46 which is pivotally secured to the flange 44 and extends through a slot 41 in plate 48, secured to arm 27. Latch arm 46 is notched as at 50 so that when the plate is rotated into the upswung position, notch 50 engages the lower edge of slot 41 and thereby serves as a support for the plate. A set screw 5| passes through an opening in the lower portion of arm 21, and engages protuberance 52 of the plate to position the plate vertically in its arc of rotation about pin 34.

In operation, a large quantity of the material to be ground is placed over rollers Ill and H, between the end gates I8. Depending upon the physical characteristics of the pigment, the end plates are adjusted lengthwise of the rolls by rotating handle 42; and the clearance space between the plates and the rollers is adjusted by manipulating bolt 31 and set screw 43. If the rollers are operated at high speed, the pigment material passing between the middle roller II and the end plates causes a substantial pressure to be built up which urges the end plates toward the second roller ll; however, the engagement of set screw 41 with flange 40 prevents the displacement of the plates beyond the position in which apex 38 is disposed directly above the line of contact of the two rollers. When the plates are in this position and the clearance spaces between the plate and the roller are properly adjusted, there is no grinding action between the plates and either rollers. Hence, there is no abrasion of the plates or rolls, no overheating of the rollers, discoloration of the pigment or excessive leakage toward the ends of the rollers.

Having described my invention I claim:

1. In a grinding mill including a pair of parallel grinding rollers in engagement with one another along a line of contact, one of said rollers being the second roller of said mill, a pail-"of plates disposed above said rollers adjacent the ends thereof, each of said plates being configur ated to form two curves meeting in an apex, 'a. rod disposed above said rollers, a pair of mounting arms depending from said rod, one of said plates being secured to each of said mounting arms, said plates and said arms being configur ated so that when said apex is disposed over said line of contact, the center of gravity of said plate is displaced from vertical alignmentwith said rod, and said apex is urged toward said second roll, means for preventing the rotation of said plates relative to said mounting arms in a direction transversely of said rolls, a set screw carried by each of said mounting arms, an abutment member extending parallel to said rod on the side of said rod adjacent said second roller, said set screws engaging said abutment member and being efiective to limit displacement of the arms and end plates in the direction of the second roller beyond a point at which the apex of each of said plates is disposed directly over the line of contact of said rollers.

2. In a grinding mill including a pair of parallel grinding rollers in engagement with one another along a line of contact, one of said rollers being the second roller of said mill, a pair of plates disposed above said rollers adjacent the ends thereof, each of said plates being configurated to form two curves meeting in an apex, means for positioning said plates so that said apex is disposed directly over the line of contact of said rollers, said means including a rod disposed above said rollers, a pair of mounting arms depending from said rod, one of said plates being carried by each of said mounting arms. said plates and said arms being configurated so that when said apex is disposed over said line of contact, the center of gravity of said plate is displaced from vertical alignment with said rod, and said apex is urged toward said second roller, a set screw associated with each of said mounting arms, an abutment member extending parallel to said rod on the side of said rod adjacent said second roller, said set screws engaging said abutment member and being effective to limit displacement of the end plates in the direction of the second roller.

3. In a grinding mill including a pair of parallel grinding rollers in engagement with one another along a line of contact, one of said rollers being the second roller of said mill, a pair of plates disposed above said rollers adjacent the ends thereof, each of said plates being con-a figurated to form two curves meeting in an apex, means for positioning said plates so that said apex is disposed directly over the line of contact of said rollers, said means including a rod disposed above said rollers, a pair of mounting arms depending from said rod, each of said arms including a boss in engagement with said rod and a portion depending from said boss, said boss being onset with respect to said depending por-,- tion in the direction of said second roller, a bracket hingedly connected to each of said arms and adapted to rotate in a plane parallel to said line of contact, said end plates being slidably mounted on said brackets, a lug on each. of said end plates in engagement with said brackets for constraining said plates to vertical movement relative to said brackets, a set screw carried by each of said mounting arms, a flange disposed parallel to said rod on the side of said rod adjacent said second roller, said set screw engaging said flange and being effective to limit displacement of said arms and the end plates in the direction of the second roller.

4. In a grinding mill including a pair of grinding rollers in engagement with one another along the line of contact, one of said rollers being the second roller of the mill, a pair of plates suspended between and at the ends of the rollers for controlling the 'endwise leakage of a pigment material disposed intermediate the plates, the lower surface of said plates being configurated to form two curves, said curves being concentric with the rollers and of a slightly larger radius, said curves meeting in an apex disposed over the line of contact of said rollers, means for supporting said plates in spaced engagement from said rollers, said means including a rod extending parallel with said line of contact, support arms depending from said rod, said plates being carried by said support arms, each of said support arms including a boss engaging said rod and a portion depending from said boss, said boss being ofiset with respect to said depending portion, each of said arms being disposed so that the depending portion is more remote from the second roller than said boss, whereby the center of gravity of said plate and said arm is not in vertical alignment with said rod and the plate is biased for rotation toward said second roller, means for preventing the displacement of said plates toward said second roller beyond a point at which said apex is disposed over said line of contact, said means including an abutment member extending parallel to said rod on the side of said rod adjacent said second roller, and set screws associated with said arms and disposed for engagement with said abutment member.

5. In a grinding mill including a pair or grinding rollers in engagement with one another along the line of contact, one of said rollers being the second roller of the mill, a pair of plates suspended between and at the ends of the rollers for controlling the endwise leakage of a pigment material disposed intermediate the plates, the

lower surface of said plates being configurated to form two curves, said curves being concentric with the rollers and of a slightly larger radius, said curves meeting in an apex disposed over the line of contact of said rollers, means for supporting said plates in spaced engagement from said rollers, said means including a rod extending parallel with said line of contact, support arms depending from said rod, said plates being carried by said support arms, each of said support arms including a boss engaging said rod and a portion depending from said boss, said boss being offset with respect to said depending portion in the direction of said second roller, said support arms being joined to said plates at a point midway between the sides thereof, means for preventing rotative movement of said plates relative to said arms in a direction perpendicular to the line of contact of said rollers, means for preventing the displacement of said plates toward said second roller beyond a point at which said apex is disposed over said line of contact, said means including an abutment member disposed parallel to said rod and lying on the side of said rod adjacent said second roller, and set screws associated with said arms and disposed for engagement with said abutment member.

6. In a grinding mill including a pair of grinding rollers in engagement with one another along the line of contact, one of said rollers being the second roller of said mill, a pair of plates suspended between and at the ends of the rollers for controlling the endwise leakage of a pigment material disposed intermediate the plates, the lower surface of said plates being configurated to form two curves, said curves being concentric with the rollers and of a slightly larger radius, said curves meeting in an apex disposed over the line of contact of said rollers, means for supporting said plates in spaced engagement from said rollers, said means including a rod extending parallel with said line of contact, support arms depending from said rod, said plates being carried by said support arms, each of said support arms including a boss engaging said rod and a portion depending from said boss, said boss being offset with respect to said dependent portion in the direction of said second roller, a bracket hingedly connected to each of said arms and adapted to rotate in a plane parallel to said line of contact, said end plates being slidably mounted on said brackets, a lug on each of said end plates in engagement with said brackets for constraining said plates to vertical movement relative to said brackets, a set screw carried by each of said mounting arms, a flange disposed parallel to said rod on the side of said rod adjacent said second roller, said set screw engaging said flange and being effective to limit displacement of said arms and the end plates in the direction of the second roller.

7. In a grinding mill including a pair of parallel grinding rollers in engagement with one another along a line of contact, one of said rollers being the second roller of said mill, a pair of plates disposed above said rollers adjacent the ends thereof, each of said plates being configurated to form two curves meeting in an apex, a rod disposed above said rollers, a pair of mounting arms depending from said rod, said arms being free to rotate about said rod, one of said plates being secured to each of said mounting arms, said plates and said arms being configurated so that when said apex is disposed over said line of contact, the center of gravity of said plate is displaced from vertical alignment with said rod and said apex is urged toward said second roll, and means for preventing rotation of said plates toward said second roll beyond a point where said apex is disposed over said line of contact.

CHARLES P. BRASINGTON.

Brasington Dec. 8, 1936 Hasson Jan. 19, 1943 Number 

